Is the playback maximum 60 fps?
The maximum fps that can be played back will depend on your computer and the complexity of the scene in blender.

The syncronze playback option tells blender to play every frame or drop frames to keep playback in sync with time. You set the fps at the 100 you want in the final output video, then if the scene can be played at 100 fps it will be, otherwise frames will be dropped so that playback will be in sync timewise.

The interface preferences can be set to display the fps that are being played, when frames are being dropped the fps will be drawn in red.